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5.4 Terminating the SCSI Chain
The SCSI chain is an electrical bus connecting two or more
devices. It is critical that this bus be correctly terminated for the
SCSI peripherals to work properly.
Termination is an electronics term that applies to the
impedance found at both ends of the bus. The electrical signals
on the SCSI bus are changing rapidly between their digital “on”
and “off” states. To minimize noise, a terminator is placed on
each end of the bus. The effects of this termination may be
subtle, but are critical to the correct operation of the scanner
on bus.
Typically, the computer is located at one end of the SCSI bus.
Assuming this is the case, the SCSI controller in the computer
has to be terminated.
Warning! Incorrect SCSI termination can cause unpredictable
errors.
If one other SCSI peripheral shares this SCSI bus, it also has to
be terminated. If additional SCSI devices are connected to the
bus between the two end SCSI devices, these devices can NOT
be terminated. Only two terminated devices can reside on the
SCSI bus, one at each end.
Improperly terminated SCSI peripherals can fail immediately or
may work correctly for a period of time before generating their
first errors.
Terminating the Internal-mount Scanner
If the LS-20 is at the end of the chain, attach the provided SCSI
terminator as described below.
The SCSI terminator is usually inserted between the SCSI
connector on the LS-20 and the provided SCSI flat cable, as
shown below.
Insert terminator
between these con-
nectors